1. Field of the Invention
The present invention relates to an electronic device, a battery pack, and an electronic device system.
2. Description of the Related Art
Some electronic devices or accessory devices attachable to electronic devices are provided with one or more battery pack compartments for mounting one or more rechargeable battery packs, respectively, and each of the electronic devices is used with one or more battery packs having a remaining capacity-detecting capability, mounted in the battery pack compartment(s)(see Japanese Patent Laid-Open Publication No. 2007-80618). In this case, resistance is different depending on a transmission line from contact terminals of the battery pack compartment and a line path through a battery switching circuit, and the power supply voltage of the electronic device supplied by the battery pack becomes lower as the resistance is larger.
The lower limit of operating voltage of the electronic device is the same condition applied to each battery, and hence if the resistance increase, a voltage drop caused by the resistance makes it impossible to use part of the whole battery capacity expected to be available from the battery pack. In a rechargeable battery pack having the remaining capacity-detecting capability, it is required to set a relative apparent or nominal available capacity of the battery pack as 100%, and therefore the part of the battery capacity that cannot be used is left uncorrected, which produces an error.
Further, a battery pack mounted in an accessory device can function as a power supply not only for an electronic device, but also for the accessory device. In such a case, when the amount of electric current consumed by the accessory device is much smaller than that of electric current consumed by the electronic device, it is impossible to measure the former by an electric current detection circuit provided in the battery pack, and hence an error is caused by the integral of electric current continuously consumed by the accessory device.
In the prior art, it is possible to detect whether or not an accessory device is attached to an electronic device, but when two or more battery packs are mounted in the electronic device and the accessory device, it is impossible to determine which of the battery packs mounted in one of the electronic device and the accessory device is supplying power. For this reason, for the battery packs mounted in the electronic device and the accessory device, it is impossible to correct differences in the aforementioned resistance separately between the battery packs, which causes an error in a result of detection of the remaining battery capacity of each battery pack.
Further, in a case where two or more battery packs are mounted in an accessory device, it is impossible to detect the configuration of the battery packs, and hence it is also impossible to determine how undetectable electric current is being consumed by which of the battery packs. Thus, the prior art cannot make it possible to accurately correct an error corresponding to the integral of undetectable electric current consumed by each of the battery packs.
Moreover, when a battery pack is mounted anew in an electronic device or in an accessory device, the prior art compels the battery pack to wait for an instruction from a control microcomputer of the electronic device before the battery pack performs remaining capacity correction, and the integral of electric current consumed at the time causes an error.